Corrected entry: When Paul is looking in the mirror and saying he's a sex machine, instead of looking at himself in the mirror, Paul is looking at the camera in the mirror. That's why his eyes in the mirror look to the front. This happens in many films and TV shows.
Corrected entry: When Paul enters his bedroom and Ross is behind the door, Ross hesitates and then snakes under the bed while Paul is distracted. However, Paul is looking at the mirror in the corner, which faces back towards the door, so he should have seen Ross standing there.
Corrected entry: At the museum, the girls learn there is a two-year waiting list for weddings. But when there is a cancellation, Monica is called about filling the spot. If there was a cancellation, wouldn't the next person on the list be called? Even if they weren't interested, there would be two years worth of couple ahead of Monica and Chandler.